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An annual soil test to determine nutrient needs for cotton is more important than ever and farmers probably should dig a little deeper to determine if they have residual nitrogen that could reduce fertility costs significantly.

Dennis Coker, Texas AgriLife Department of Soil And Crop Science, says cotton producers have to be careful not to leave out essential nutrients but can manage crop fertility better when they know what’s already in the soil.

He recommends annual soil tests “because of increased fertilizer costs and the need to know what’s in the soil bank. The soil bank is a season-long resource,” he said.

Coker, speaking at the recent Texas Plant Protection Association annual conference in College Station, said several factors affect availability of some nutrients in the soil. Rainfall, variety selection, day and nighttime temperatures, soil texture, pH and organic matter content all may affect nutrient uptake, leaching potential and volatilization.

Price volatility is a good reason to soil test, he said. Since 2003 the price of anhydrous ammonia has increased from 15 cents a pound to 35 cents a pound; urea has gone from 27 cents a pound to 54 cents a pound; and UAN 32 has increased from 28 cents a pound in 2003 to 62 cents a pound in 2011, and that’s down from 2008.

He said the 2011 drought may have left nitrogen in the soil. “We had a lot of cotton planted in exceptional drought areas,” he said. A lot of corn also failed, possibly leaving residual nitrogen. “In any given season, a certain amount of nutrients are removed by crops,” Coker said. But some nutrients, such as phosphorus, potassium, calcium, magnesium, sulfur and micronutrients might carry over.